If a belt-driven reciprocating air compressor is operating at a lower than design displacement capacity (in cubic feet per minute), which of the following would be a cause?

Correct Answer: Option A — Insufficiently tensioned drive belts.

Insufficient belt tension causes slippage between the motor sheave and the compressor flywheel. This slippage prevents the compressor from reaching its design rotational speed (RPM), directly reducing the volume of air moved per unit of time, thereby lowering the overall displacement capacity of the unit.